The present invention generally relates to image transfer technology and, more particularly, to an apparatus and method for monitoring a marking liquid in an image transfer device, and an image transfer device utilizing the apparatus and method.
As used herein, the term “image transfer device” generally refers to all types of devices and systems used for creating and/or transferring an image in an imaging process, including laser printers, copiers, facsimiles, and the like. An electrophotographic process is one exemplary imaging process. As used herein, the term “electrophotographic process” includes both dry and liquid electrophotographic (LEP) processes.
In an electrophotographic image transfer device, the surface of a photoconducting material (i.e., a photoreceptor) is charged to a substantially uniform electrostatic potential so as to sensitize the surface. An electrostatic latent image is created on the surface of the charged photoconducting material by selectively exposing areas of the photoreceptor surface to a light image of the original document being reproduced. A difference in electrostatic charge density is created between the areas on the photoreceptor surface exposed and unexposed to light. The electrostatic latent image on the photoreceptor surface is developed into a visible image using electrostatic toners or pigments. The toners are selectively attracted to the photoreceptor surface either exposed or unexposed to light, depending on the relative electrostatic charges of the photoreceptor surface, development electrode, and toner. The photoreceptor surface may be either positively or negatively charged, and the toner system similarly may contain negatively or positively charged particles. An intermediate transfer member is passed close to the photoreceptor surface, which may be in the form of a rotating drum or belt, transferring the toner from the photoreceptor surface onto the intermediate transfer member in the pattern of the image developed on the photoreceptor surface, A sheet of paper or other medium is then passed close to the intermediate transfer member, which may be in the form of a rotating drum or belt, transferring the toner from the intermediate transfer member onto the paper, thereby forming a hard image. In some image transfer devices, no intermediate transfer member is used, and the paper or other medium is passed close to the photoreceptor surface to form a hard image.
In some image transfer devices, the toners or pigments used to develop the electrostatic latent image on the photoreceptor surface are delivered to the photoreceptor surface in a suspension or dispersion with another material that acts as a carrier or vehicle for the toners or pigments. In such systems, there are process and material parameters that need to be stabilized at consistent and well-controlled values to ensure a high image quality. For example, the concentration of toners or pigments in the carrier affects the quality of the hard image produced by the image transfer device, as does the temperature of the carrier and toners or pigments therein. If these parameters go outside of a desired range, the quality of the hard image is adversely impacted. Accordingly, sensors for determining the concentration of particles (e.g., toners or pigments) in the carrier, temperature, and other material or process parameters (e.g., conductivity, fluid level, etc.) may be utilized.
Methods and apparatuses for determining particle concentration, temperature, and other material or process parameters in image transfer devices are known and successfully implemented, However, improved methods and apparatuses for determining particle concentration and temperature are always desirable. Improved methods and apparatuses may reduce complexity, reduce costs, improve accuracy, require less frequent calibration, require less cleaning, be less sensitive to color cross-contamination, or provide a greater range of measurement.